CA1233147A - Diffuser for a centrifugal compressor - Google Patents
Diffuser for a centrifugal compressorInfo
- Publication number
- CA1233147A CA1233147A CA000468496A CA468496A CA1233147A CA 1233147 A CA1233147 A CA 1233147A CA 000468496 A CA000468496 A CA 000468496A CA 468496 A CA468496 A CA 468496A CA 1233147 A CA1233147 A CA 1233147A
- Authority
- CA
- Canada
- Prior art keywords
- section
- diffuser
- sidewalls
- throat portion
- linear
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/40—Casings; Connections of working fluid
- F04D29/42—Casings; Connections of working fluid for radial or helico-centrifugal pumps
- F04D29/44—Fluid-guiding means, e.g. diffusers
- F04D29/441—Fluid-guiding means, e.g. diffusers especially adapted for elastic fluid pumps
- F04D29/444—Bladed diffusers
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2250/00—Geometry
- F05D2250/50—Inlet or outlet
- F05D2250/52—Outlet
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Structures Of Non-Positive Displacement Pumps (AREA)
Abstract
DIFFUSER FOR A CENTRIFUGAL COMPRESSOR
ABSTRACT OF THE DISCLOSURE
The diffuser of the present invention comprises a plurality of passages which intersect at radially inner ends thereof to define a quasi-vaneless annular inlet for receiving accelerated gases from an impeller of a centrifugal compressor. Each of the passages includes a throat portion having a quadrilateral cross section, including two substantially parallel linear sidewalls and two substantially arcuate opposing sidewalls, effective for reducing the length of and thereby pressure losses from the annular inlet. The linearity and regularity of the diffuser passages enables the diffuser to be manufactured to close tolerances by electric discharge milling an annular plate utilizing a single tool. This assures uniformity and consistency between diffusers.
ABSTRACT OF THE DISCLOSURE
The diffuser of the present invention comprises a plurality of passages which intersect at radially inner ends thereof to define a quasi-vaneless annular inlet for receiving accelerated gases from an impeller of a centrifugal compressor. Each of the passages includes a throat portion having a quadrilateral cross section, including two substantially parallel linear sidewalls and two substantially arcuate opposing sidewalls, effective for reducing the length of and thereby pressure losses from the annular inlet. The linearity and regularity of the diffuser passages enables the diffuser to be manufactured to close tolerances by electric discharge milling an annular plate utilizing a single tool. This assures uniformity and consistency between diffusers.
Description
~33~
. . .
DIFFUSER FOR A CENT~IFUG~`L COMPRESSOR
BAC~GROUND OF THE INVENTION
The invention relates to a diffuser and, more particularly, to a diffuser for a centrifugal compressor which is configured to optimize flow distributinn to a combustion chamber and which may be manufactured to close`tolerances in a manner which assures uniformity between diffusers.
A centriu~al compressor includes a rotating impeller arranged to accelerate and thereb~y increase the kinetic energy of a gas flowing therethrough. The diffuser is ~enerally characteriæed by a quasi-vaneless annular space surrounding the impeller. The diffuser acts to decrease the velocity of the gas flow leaving the impeller to transform the energy thereof to an increase in static pressure, thus generating pressurized gas.
Prior art diffusers have generally included a plurality of circumferentially spaced passages which converge to the annular space surrounding the impeller.
These passages expand in area downstream of the impeller in order to diffuse the flow exiting the impeller. It has been found for prior art diffusers of this type which are to be utilized with gas turbine engines that it is preferable to have the diffuser passages assume ... .
~23~
an initial circular cross section so as to accommodate with minimal losses the relatively high-flow velocities of the gases e~iting the impeller and thereafter gradually merge into a near-rectangular outlet to minimize losses.
One diffuser of this type is disclosed in U. S.
Patent 4,027,997 issued to A, C. sryans on 7 June 1977, and assigned to the assignee of this invention. The Bryans diffuser comprises a plurality of linear passages in flow cGmmunication with a quasi-vaneless annular inlet surroundin~ the impeller of a centrifugal compressor.
Each passage gradually merges from a circular cross section at a throat portion near its inlet end, to a near rectangular cross section at its outlet end defined by two flat opposing parallel sides and t~o flat opposing curved sides which produce a razor sharp trailing edge at the diffuser outlet. This near rectangular shape of the diffuser outlet optimizes the flow distribution to an annular combustion chamber in flow communication with the diffuser outlet~
Diffusers constructed in accordance with the teachings of the Bryans patent have demonstrated significant improvements in the performance of centrifugal compressors ~or gas turbine engines. However, inasmuch as the quasi-vaneless inlet of the diffuser receives accelerated gases directly from the impeller, it i5 subject to relatively high viscous drag which results in undesirable pressure losses.
Accordingly, it is an object of the present invention to provide a new and improved diffuser for a centrifugal compressor.
Another object of the present invention is to provide a diffuser wherein the len~th of the quasi vaneless inlet is reduced for reducing the total of ~5 viscous drag thereover.
~33~7 Another object of the present invention is to provide a diffuser for a centrifugal compressor which is configured to optimize flow distribution to a combustion chamber and which may be easily manufactured to close tolerances in a manner which assures uniformity between diffusers, SUMMARY OF THE INVENTION
... ..~
The diffuser of the present invention comprises a plurality of passages which intersect at radially inner ends thereof to define a quasi-vaneless annular inlet for receiving accelerated gases from an impeller of a centrifugal compressor. Each of the passages includes a throat portion having a quadrilateral cross section, including two substantially parallel linear sidewalls and two substantially arcuate opposing sidewalls, effective for reducing the length of and thereby pressure losses from the annular inlet. The linearity and regularity of the diffuser passages enables the diffuser to be - manufactured to close tolerances by electric discharge milling an annular plate utilizing a single tool. This assures uniformity and consistency between diffusers~
B~IEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth in the appended claims~ The invention itself, together with further objects and advantages thereof, is more particularly described in the ~ollowing detailed description taken in conjunction with the accompanying drawings in which:
Figure 1 is a fragmentary sectional view of a compressor including a diffuser in accordance with the present invention.
Figure 2 is a sectional view taken along tKe line 2 - 2 of Figure 1~
Figure 3 is a diagrammatic view illustrating ~nd comparing the intersection of a passage having a ~ 33~
, throat portion in accordance with this invention and a passage of equal area having a circular cross section.
Figure 4 is a sectional view taken along line 4 - 4 of Figure 1.
Figure 5 is a sectional view taken along line 5 - 5 of Figure 1.
Figure 6 i5 a sectional view taken along line 6 - 6 of Figure 1.
Figure 7 is a perspective view of an exemplary EDM electrode suitable for machining a passa~e similar to the ones illustrated in Figure 1.
DETAILED DESCRIPTION
Illustrated in Figure 1 is a fragmen-tary sectional view of a centrifugal compressor 10 which is effective for pressuring air to a combustion chamber of a conventional gas turbine engine (not shown). The compressor 10 includes an annular impeller 12 in flo~ communication with an improved annular diffuser 14 according to one embodiment of the present invention disposed radially outwardly thereof~ Centri$ugal compressors are well known in the art for converting the relatively high kinetic energy of gases accelerated by the rotating impeller 12 into static-pressure energy. The diffuser 14 according to the present invention, however, represents an improvement over conventional diffusers, and, in particular, over the above-described diffuser disclosed in U. S. Patent 4,027,997 - A. C. sryans.
The conventional impeller 12 includes a plurality of circumferentially spaced impeller blades 16 supported by an annular web 18. The diffuser 14 includes an annular diffuser housing 20 having a plurality of tangentially disposed flow passages 22, which are disposed along linear centerlines, spaced about the circumference of the housing 20 and extending therethrough. The passages 22 are partly defined and bounded by a plurality of spacecl, 31~
5 - ~
generally convex vanes 23. Adjacent ones of the passages 22 intersect with each other at radially inner, inlet portions 24 that define a quasi-vaneless annular inlet 26 of the diffuser 14. Each passage 22 further includes a throat portion 28 which i9 integral with the inlet portion 24 and has a first quadrilateral cross section 30, which defines the flow passage thereof, including: two substantially parallel linear opposing sidewa].ls 32 and 34 and two substantially arcuate opposing sidewalls 36 and 38 ~see Figure 2).
As illustrated in Figures 1, 4 and 5, the inlet portion 24 is a partially bounded passage having a generally semi-circular cross section, open at an apex thereof, at its upstream end which tapers to a generally flat, linear-sided section at its downstream end where it intersects with the throat portion 28. The throat portion 28 represents the first fully bounded flow portion of the passage 22. The annular inlet 26 is defined as ~uasi-vaneless because the vanes 23 primarily end at the upstream end of the throat portion 28 with only relatively small lip or step portions 23a and 23b extending and tapering from the throat portion 28 to the upstream end of the inlet portion 24.
A significant feature of the present invention is the introduction of the step portions 23a and 23b in the inlet portion 24, as illustrated in Figure 5, which include flat, radially outwardly facing surfaces represented by portions of the sidewall 32 and arcuate, radially inwardly facing surfaces represented by portions of the sidewalls 36 and 33. The flat surfaces o-f step portions 23a and 23b act as walls to help confine airflow in the quasi-vaneless inlet 26 for reducing distortion thereof and the possibility of stall therein.
More specifically, it will be appreciated that pressure of the airflow in the inlet 26 increases in a ~33~
radially outward direction. ~Iigher pressure at radially outer portions will tend to cause the boundary layer found along the walls of the inlet 26 to be forced radially inwardly, which can possibly lead to stall.
Accordingly, the flat surfaces of the step portions 23a and 23b will assist in preventing the boundary layer from being driven toward the impeller, thusly reducing the likelihood of stall, thereby increasing stall margin, and allowing for increased performance of the diffuser 14.
The throat portion 28 according to the present invention represents a significant improvement in the aerodynamic eficiency of the diffuser 14. More specifically, it is conventional to design a compressor considering engine performance~ pressure ratio and flow volumes~ for exampler for determining the required quantity of the plurality of tangentially disposed diffuser passages 22, the required flow area A of the throat portions 2~ and the width 2b of radially outer tip ends of the impeller blades 16 (see Figure 5). With the throat flow area A be.ing known, a particular shape or cross section of the throat portion 28 is then determined.
In conventional high-performance diffusers, a circular profile of the throat portion 28 is preferred. ~Iowever, in accordance with the present inyention, it has been determined that the throat portion 28 having the quadrilaterial cross section 30, wherein the spacing between the sidewalls 32 and 34 is less than the diameter of an equal area circle, provides for improved aerodynamic performance of the diffuser 14.
More specifically, and referring to ~igures 1, 4 r and 5, the inlet portion 24 of the passages 22 is illustrated a~.d has a length Ll . It will be appreciated that the inlet portion 24 receives gases from the impeller 12 at relatively high velocities and relatively low pressures, and. is therefore subject to relatively high 1;;~33~
viscous dragA Accordingly, it has been discovered that any reduction in the length of Ll of the inlet portion 24 will decrease the surface area subject to relatively high visco~us drag and therefore result in a decrease of the total viscous drag.
Figure 3 represents a diagram which illustrates more clearly how the first quadrilateral cross section 30 of the throat portion 28 is effective for obtaining a reduced length Ll of the inlet 24. The circle of tangency of the centerlines of the plurality of passages 22 is shown and has a radius r, which radius r is substantially equal to the radius of the impeller 12.
Also illustra-ted are two adjacent intersecting passages having superimposed cross sections: the first quadrilateral cross section 30 and a reference, circular cross section 40 sharing common tangential centerlines, both of which have a cross-sectional area equal to A.
It will be appreciated that passages having a circular cross section 40 will intersect with each other at a distance L2 measured perpendicularly with respect to the radius r at the point of tangency of the centerline of the top passage. In contrast, passages having the first quadrilateral cross section 30 would intersect with each other at a distance Ll, wherein Ll is substantially less than L2. Accordingly, for a given cross-sectional flow area A, a throat portion 23 having the first quadrilateral cross section 30 instead of a circular cross section 40 will result in an inlet portion 24 having a reduced length Ll for reducing viscous drag forces~
The preferred dimensions of the first quadrilateral cross section 30 have been selected for not only reducin~
the length Ll of the inlet portions 24 but also for retaining part of the circular cross section, which circular sections have`proven effective for reducing ~Z33~7 losses due to flow separation.
It will be appreciated that circular cross sections have been conventionally preferred because for a given cross-sectional area they represent the least wetted surface, i.e. the circ~nferential length, subject to drag forces. In contrast, a purely rectangular cross section of the same area has a wetted surface, i.e. the perimeter length, which is greater, and, which, therefore, results in greater drag losses.. The quadrilateral cross section 30 retains benefits of the circular cross section in the arcuate sidewalls 36 and 38, yet is also efEective -to reduce the length Ll as above described.
More specifically, and referring to Figures 2 and 5, the linear sidewalls 32 and 34 are spaced from each other a distance 2b.
The arcuate sidewalls 36 and 38 of the first quadrilateral cross sectlon 30 are defined by a radius R which is determined from the solution of the integral equation:
A = 4 ~ ~ dx The solution o$ this integral equation is:
_ _ 2 lx b A = 2 x ~ 2 _ x2 + R Sin R o and applying the bounds of integration results in:
A = 2 (~ ~ + R2Sin~lR ) The solution o$ this integral equation is obtained using conventional techniques. In the integral equation, 'IA" represents the designed-for flow area of the throat portion 28, which is conventionally determined. "x" represents the distance measured outwardly from the center of the first quadrilateral cross section 30 between the two linear sidewalls 32 and 34, and "b" represents one half the spacing between sidewalls 32 and 34.
The distance between the two linear sidewalls 32 and 34 has a value equal to 2b, which is preEerably equal to the tip width of the impeller blades 16, and with the radius R of the -two arcuate sidewalls 36 and 38 determined as above described, the first quadrila-teral cross ~233~
. ~
section 30 is thereby defined completely.
As illustrated in Figure.s 1 and 4, the throat portion 28, which represents the first fully enclosed portion of the passage 22 which receives gases accelerated by the impeller 12, extends in a tangential direction, a fini.te length L3~ The length L3 is chosen so that as the throat portion 28 erodes from wear, the preferred f.irst quadrilateral cross section 30 is maintained for the designed-for life. Accordingly~ the length L3 may be made generally equal to the diameter of a circle having an area equal to the area A of the ~irst quadrilateral cross section 30 oE the throat portion 28.
Referring again to Fi~ure 1, it will be seen that each of the passages 22 further includes a diffuser portion 42 which is integral with the throat portion 28.
At a downstream end/ the diffuser portion 42 has a second quadrilateral cross section 44 including two substantially parallel opposing linèar sidewalls 46 and 48 and two substantially arcuate opposing sidewalls 50 and 52 (see Figure 6). The diffuser portion 42 has an upstream end integral with the throat portion 28 which includes a third quadrilateral cross section 54 which is substantially identical to the first quadrilateral cross section 30 of the throat portion 2g. The diffuser portion 42 is gradually tapered between its upstream and downstream ends.
As illustrated in Figures 2 and 6, the second quadrilateral cross section 4~ of the diffuser section 42 is oriented substantially 90 degrees with respect to the first quadrilateral cross section 30~ As illustxated in Figure 5, the linear sidewalls 32 and 34 of the first quadrilateral cross section 30 of the throat portion 28 are disposed substantially parallel to the tips of impeller blades 16 and substantially normal to a radial axis of the dif~user 14.
The improved diffuser 14 according to this ~233~L7 inven-tion lends itself to reIativeIy inexpensive manufacturing techniques which can maintain close tolerances and uniformity between diffusexs. Inasmuch as the centerline as well as the walls of the diffuser passages 22 may be linear and make gradual and smooth transitions, the diffuser 14 may be easily manufactured by known electric discharge milling (EDM) techniques.
More specifically~ an exemplary EDM electrode 56 is suitable for manufacturing passages generally similar to the diffuser passages 22 is illustrated in Figure 7 and can be very accurately machined firstly on a lathe with appropriate cylindrical, conical and curved sections.
Portions of the electrode 56 which create the features of the passages 22 axe identified by using the corresponding reference numerals of the passages 22. To easily and accurately obtain the first and second ~uadrilateral cross sections 3~ and 44, the linear sidewalls 32, 34, 44 and 46 may be simply and ac~urately machined or planed off in a tapered manner for obtainin~ relatively smooth transitions.
While a preferred embodiment of the present invention has been disclosed, it will be understood that many modifications and changes may be made thereto without departing from the scope of the invention as defined in the intended claims.
. . .
DIFFUSER FOR A CENT~IFUG~`L COMPRESSOR
BAC~GROUND OF THE INVENTION
The invention relates to a diffuser and, more particularly, to a diffuser for a centrifugal compressor which is configured to optimize flow distributinn to a combustion chamber and which may be manufactured to close`tolerances in a manner which assures uniformity between diffusers.
A centriu~al compressor includes a rotating impeller arranged to accelerate and thereb~y increase the kinetic energy of a gas flowing therethrough. The diffuser is ~enerally characteriæed by a quasi-vaneless annular space surrounding the impeller. The diffuser acts to decrease the velocity of the gas flow leaving the impeller to transform the energy thereof to an increase in static pressure, thus generating pressurized gas.
Prior art diffusers have generally included a plurality of circumferentially spaced passages which converge to the annular space surrounding the impeller.
These passages expand in area downstream of the impeller in order to diffuse the flow exiting the impeller. It has been found for prior art diffusers of this type which are to be utilized with gas turbine engines that it is preferable to have the diffuser passages assume ... .
~23~
an initial circular cross section so as to accommodate with minimal losses the relatively high-flow velocities of the gases e~iting the impeller and thereafter gradually merge into a near-rectangular outlet to minimize losses.
One diffuser of this type is disclosed in U. S.
Patent 4,027,997 issued to A, C. sryans on 7 June 1977, and assigned to the assignee of this invention. The Bryans diffuser comprises a plurality of linear passages in flow cGmmunication with a quasi-vaneless annular inlet surroundin~ the impeller of a centrifugal compressor.
Each passage gradually merges from a circular cross section at a throat portion near its inlet end, to a near rectangular cross section at its outlet end defined by two flat opposing parallel sides and t~o flat opposing curved sides which produce a razor sharp trailing edge at the diffuser outlet. This near rectangular shape of the diffuser outlet optimizes the flow distribution to an annular combustion chamber in flow communication with the diffuser outlet~
Diffusers constructed in accordance with the teachings of the Bryans patent have demonstrated significant improvements in the performance of centrifugal compressors ~or gas turbine engines. However, inasmuch as the quasi-vaneless inlet of the diffuser receives accelerated gases directly from the impeller, it i5 subject to relatively high viscous drag which results in undesirable pressure losses.
Accordingly, it is an object of the present invention to provide a new and improved diffuser for a centrifugal compressor.
Another object of the present invention is to provide a diffuser wherein the len~th of the quasi vaneless inlet is reduced for reducing the total of ~5 viscous drag thereover.
~33~7 Another object of the present invention is to provide a diffuser for a centrifugal compressor which is configured to optimize flow distribution to a combustion chamber and which may be easily manufactured to close tolerances in a manner which assures uniformity between diffusers, SUMMARY OF THE INVENTION
... ..~
The diffuser of the present invention comprises a plurality of passages which intersect at radially inner ends thereof to define a quasi-vaneless annular inlet for receiving accelerated gases from an impeller of a centrifugal compressor. Each of the passages includes a throat portion having a quadrilateral cross section, including two substantially parallel linear sidewalls and two substantially arcuate opposing sidewalls, effective for reducing the length of and thereby pressure losses from the annular inlet. The linearity and regularity of the diffuser passages enables the diffuser to be - manufactured to close tolerances by electric discharge milling an annular plate utilizing a single tool. This assures uniformity and consistency between diffusers~
B~IEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth in the appended claims~ The invention itself, together with further objects and advantages thereof, is more particularly described in the ~ollowing detailed description taken in conjunction with the accompanying drawings in which:
Figure 1 is a fragmentary sectional view of a compressor including a diffuser in accordance with the present invention.
Figure 2 is a sectional view taken along tKe line 2 - 2 of Figure 1~
Figure 3 is a diagrammatic view illustrating ~nd comparing the intersection of a passage having a ~ 33~
, throat portion in accordance with this invention and a passage of equal area having a circular cross section.
Figure 4 is a sectional view taken along line 4 - 4 of Figure 1.
Figure 5 is a sectional view taken along line 5 - 5 of Figure 1.
Figure 6 i5 a sectional view taken along line 6 - 6 of Figure 1.
Figure 7 is a perspective view of an exemplary EDM electrode suitable for machining a passa~e similar to the ones illustrated in Figure 1.
DETAILED DESCRIPTION
Illustrated in Figure 1 is a fragmen-tary sectional view of a centrifugal compressor 10 which is effective for pressuring air to a combustion chamber of a conventional gas turbine engine (not shown). The compressor 10 includes an annular impeller 12 in flo~ communication with an improved annular diffuser 14 according to one embodiment of the present invention disposed radially outwardly thereof~ Centri$ugal compressors are well known in the art for converting the relatively high kinetic energy of gases accelerated by the rotating impeller 12 into static-pressure energy. The diffuser 14 according to the present invention, however, represents an improvement over conventional diffusers, and, in particular, over the above-described diffuser disclosed in U. S. Patent 4,027,997 - A. C. sryans.
The conventional impeller 12 includes a plurality of circumferentially spaced impeller blades 16 supported by an annular web 18. The diffuser 14 includes an annular diffuser housing 20 having a plurality of tangentially disposed flow passages 22, which are disposed along linear centerlines, spaced about the circumference of the housing 20 and extending therethrough. The passages 22 are partly defined and bounded by a plurality of spacecl, 31~
5 - ~
generally convex vanes 23. Adjacent ones of the passages 22 intersect with each other at radially inner, inlet portions 24 that define a quasi-vaneless annular inlet 26 of the diffuser 14. Each passage 22 further includes a throat portion 28 which i9 integral with the inlet portion 24 and has a first quadrilateral cross section 30, which defines the flow passage thereof, including: two substantially parallel linear opposing sidewa].ls 32 and 34 and two substantially arcuate opposing sidewalls 36 and 38 ~see Figure 2).
As illustrated in Figures 1, 4 and 5, the inlet portion 24 is a partially bounded passage having a generally semi-circular cross section, open at an apex thereof, at its upstream end which tapers to a generally flat, linear-sided section at its downstream end where it intersects with the throat portion 28. The throat portion 28 represents the first fully bounded flow portion of the passage 22. The annular inlet 26 is defined as ~uasi-vaneless because the vanes 23 primarily end at the upstream end of the throat portion 28 with only relatively small lip or step portions 23a and 23b extending and tapering from the throat portion 28 to the upstream end of the inlet portion 24.
A significant feature of the present invention is the introduction of the step portions 23a and 23b in the inlet portion 24, as illustrated in Figure 5, which include flat, radially outwardly facing surfaces represented by portions of the sidewall 32 and arcuate, radially inwardly facing surfaces represented by portions of the sidewalls 36 and 33. The flat surfaces o-f step portions 23a and 23b act as walls to help confine airflow in the quasi-vaneless inlet 26 for reducing distortion thereof and the possibility of stall therein.
More specifically, it will be appreciated that pressure of the airflow in the inlet 26 increases in a ~33~
radially outward direction. ~Iigher pressure at radially outer portions will tend to cause the boundary layer found along the walls of the inlet 26 to be forced radially inwardly, which can possibly lead to stall.
Accordingly, the flat surfaces of the step portions 23a and 23b will assist in preventing the boundary layer from being driven toward the impeller, thusly reducing the likelihood of stall, thereby increasing stall margin, and allowing for increased performance of the diffuser 14.
The throat portion 28 according to the present invention represents a significant improvement in the aerodynamic eficiency of the diffuser 14. More specifically, it is conventional to design a compressor considering engine performance~ pressure ratio and flow volumes~ for exampler for determining the required quantity of the plurality of tangentially disposed diffuser passages 22, the required flow area A of the throat portions 2~ and the width 2b of radially outer tip ends of the impeller blades 16 (see Figure 5). With the throat flow area A be.ing known, a particular shape or cross section of the throat portion 28 is then determined.
In conventional high-performance diffusers, a circular profile of the throat portion 28 is preferred. ~Iowever, in accordance with the present inyention, it has been determined that the throat portion 28 having the quadrilaterial cross section 30, wherein the spacing between the sidewalls 32 and 34 is less than the diameter of an equal area circle, provides for improved aerodynamic performance of the diffuser 14.
More specifically, and referring to ~igures 1, 4 r and 5, the inlet portion 24 of the passages 22 is illustrated a~.d has a length Ll . It will be appreciated that the inlet portion 24 receives gases from the impeller 12 at relatively high velocities and relatively low pressures, and. is therefore subject to relatively high 1;;~33~
viscous dragA Accordingly, it has been discovered that any reduction in the length of Ll of the inlet portion 24 will decrease the surface area subject to relatively high visco~us drag and therefore result in a decrease of the total viscous drag.
Figure 3 represents a diagram which illustrates more clearly how the first quadrilateral cross section 30 of the throat portion 28 is effective for obtaining a reduced length Ll of the inlet 24. The circle of tangency of the centerlines of the plurality of passages 22 is shown and has a radius r, which radius r is substantially equal to the radius of the impeller 12.
Also illustra-ted are two adjacent intersecting passages having superimposed cross sections: the first quadrilateral cross section 30 and a reference, circular cross section 40 sharing common tangential centerlines, both of which have a cross-sectional area equal to A.
It will be appreciated that passages having a circular cross section 40 will intersect with each other at a distance L2 measured perpendicularly with respect to the radius r at the point of tangency of the centerline of the top passage. In contrast, passages having the first quadrilateral cross section 30 would intersect with each other at a distance Ll, wherein Ll is substantially less than L2. Accordingly, for a given cross-sectional flow area A, a throat portion 23 having the first quadrilateral cross section 30 instead of a circular cross section 40 will result in an inlet portion 24 having a reduced length Ll for reducing viscous drag forces~
The preferred dimensions of the first quadrilateral cross section 30 have been selected for not only reducin~
the length Ll of the inlet portions 24 but also for retaining part of the circular cross section, which circular sections have`proven effective for reducing ~Z33~7 losses due to flow separation.
It will be appreciated that circular cross sections have been conventionally preferred because for a given cross-sectional area they represent the least wetted surface, i.e. the circ~nferential length, subject to drag forces. In contrast, a purely rectangular cross section of the same area has a wetted surface, i.e. the perimeter length, which is greater, and, which, therefore, results in greater drag losses.. The quadrilateral cross section 30 retains benefits of the circular cross section in the arcuate sidewalls 36 and 38, yet is also efEective -to reduce the length Ll as above described.
More specifically, and referring to Figures 2 and 5, the linear sidewalls 32 and 34 are spaced from each other a distance 2b.
The arcuate sidewalls 36 and 38 of the first quadrilateral cross sectlon 30 are defined by a radius R which is determined from the solution of the integral equation:
A = 4 ~ ~ dx The solution o$ this integral equation is:
_ _ 2 lx b A = 2 x ~ 2 _ x2 + R Sin R o and applying the bounds of integration results in:
A = 2 (~ ~ + R2Sin~lR ) The solution o$ this integral equation is obtained using conventional techniques. In the integral equation, 'IA" represents the designed-for flow area of the throat portion 28, which is conventionally determined. "x" represents the distance measured outwardly from the center of the first quadrilateral cross section 30 between the two linear sidewalls 32 and 34, and "b" represents one half the spacing between sidewalls 32 and 34.
The distance between the two linear sidewalls 32 and 34 has a value equal to 2b, which is preEerably equal to the tip width of the impeller blades 16, and with the radius R of the -two arcuate sidewalls 36 and 38 determined as above described, the first quadrila-teral cross ~233~
. ~
section 30 is thereby defined completely.
As illustrated in Figure.s 1 and 4, the throat portion 28, which represents the first fully enclosed portion of the passage 22 which receives gases accelerated by the impeller 12, extends in a tangential direction, a fini.te length L3~ The length L3 is chosen so that as the throat portion 28 erodes from wear, the preferred f.irst quadrilateral cross section 30 is maintained for the designed-for life. Accordingly~ the length L3 may be made generally equal to the diameter of a circle having an area equal to the area A of the ~irst quadrilateral cross section 30 oE the throat portion 28.
Referring again to Fi~ure 1, it will be seen that each of the passages 22 further includes a diffuser portion 42 which is integral with the throat portion 28.
At a downstream end/ the diffuser portion 42 has a second quadrilateral cross section 44 including two substantially parallel opposing linèar sidewalls 46 and 48 and two substantially arcuate opposing sidewalls 50 and 52 (see Figure 6). The diffuser portion 42 has an upstream end integral with the throat portion 28 which includes a third quadrilateral cross section 54 which is substantially identical to the first quadrilateral cross section 30 of the throat portion 2g. The diffuser portion 42 is gradually tapered between its upstream and downstream ends.
As illustrated in Figures 2 and 6, the second quadrilateral cross section 4~ of the diffuser section 42 is oriented substantially 90 degrees with respect to the first quadrilateral cross section 30~ As illustxated in Figure 5, the linear sidewalls 32 and 34 of the first quadrilateral cross section 30 of the throat portion 28 are disposed substantially parallel to the tips of impeller blades 16 and substantially normal to a radial axis of the dif~user 14.
The improved diffuser 14 according to this ~233~L7 inven-tion lends itself to reIativeIy inexpensive manufacturing techniques which can maintain close tolerances and uniformity between diffusexs. Inasmuch as the centerline as well as the walls of the diffuser passages 22 may be linear and make gradual and smooth transitions, the diffuser 14 may be easily manufactured by known electric discharge milling (EDM) techniques.
More specifically~ an exemplary EDM electrode 56 is suitable for manufacturing passages generally similar to the diffuser passages 22 is illustrated in Figure 7 and can be very accurately machined firstly on a lathe with appropriate cylindrical, conical and curved sections.
Portions of the electrode 56 which create the features of the passages 22 axe identified by using the corresponding reference numerals of the passages 22. To easily and accurately obtain the first and second ~uadrilateral cross sections 3~ and 44, the linear sidewalls 32, 34, 44 and 46 may be simply and ac~urately machined or planed off in a tapered manner for obtainin~ relatively smooth transitions.
While a preferred embodiment of the present invention has been disclosed, it will be understood that many modifications and changes may be made thereto without departing from the scope of the invention as defined in the intended claims.
Claims (20)
1. A diffuser for a centrifugal compressor having an impeller comprising:
an annular housing;
a plurality of passages spaced about the circum-ference of said housing and extending therethrough, adjacent ones of said passages intersecting with each other at radially inner inlet portions thereof for defining a quasi-vaneless annular inlet of said diffuser, each of said passages further including a throat portion integral with said inlet portion, said throat portion having a first quadrilateral cross section including two substaantially parallel linear opposing sidewalls and two substantially arcuate opposing sidewalls, said two linear sidewalls being spaced from each other to define a minor dimension extending therebetween, said two arcuate sidewalls being spaced from each other to define a major dimension therebetween, said major dimension being greater in length than said minor dimension, and said linear sidewalls being disposed substantially normal with respect to a radial axis of said diffuser.
an annular housing;
a plurality of passages spaced about the circum-ference of said housing and extending therethrough, adjacent ones of said passages intersecting with each other at radially inner inlet portions thereof for defining a quasi-vaneless annular inlet of said diffuser, each of said passages further including a throat portion integral with said inlet portion, said throat portion having a first quadrilateral cross section including two substaantially parallel linear opposing sidewalls and two substantially arcuate opposing sidewalls, said two linear sidewalls being spaced from each other to define a minor dimension extending therebetween, said two arcuate sidewalls being spaced from each other to define a major dimension therebetween, said major dimension being greater in length than said minor dimension, and said linear sidewalls being disposed substantially normal with respect to a radial axis of said diffuser.
2. A diffuser according to claim 1 wherein said first quadrilateral cross section has an area and said linear opposing sidewalls are spaced from each other a distance less than the diameter of a circle having an area equal to said quadrilateral area.
3. A diffuser according to claim 1 wherein said linear sidewalls are spaced from each other a distance 2b, each of said arcuate sidewalls of said throat portion is defined by a radius R extending from a center point of said throat portion, said throat portion has a cross sectional area A, and R, A and b are related to each other as follows:
4. A diffuser according to claim 3 wherein said distance b represents one half the tip width of blades of said impeller.
5. A diffuser according to claim 1 wherein said throat portion extends with a constant area in a tangential direction for a length generally equal to the diameter of a circle having an area equal to the area of said first quadrilateral cross section of said throat portion.
6. A diffuser according to claim 1 wherein said plurality of passages further includes a diffuser portion integral with said throat portion and having at a downstream end a second quadrilateral cross section including two substantially parallel opposing linear sidewalls and two substantially acruate opposing sidewalls.
7. A diffuser according to claim 6 wherein said diffuser portion further includes at an upstream end a third quadrilateral cross section substantially identical to said first quadrilateral cross section of said throat portion, said diffuser portion being gradually tapered between said upstream and downstream ends.
8. A diffuser according to claim 6 wherein said second quadrilateral cross section is oriented substantially 90 degrees with respect to said first quadrilateral cross section.
9. A diffuser according to claim 1 wherein each of said inlet portions defines a partially bounded passage having a generally semi-circular cross section at an upstream end thereof which is open at opposing base and apex portions thereof, said inlet portion tapering from said semi-circular cross section to said first quadrilateral cross section of said throat portion.
10. A diffuser according to claim 9 wherein said adjacent ones of said inlet portions intersect with each other to define step portions extending and tapering from said throat portion to said upstream end of said inlet portion.
11. A diffuser according to claim 10 wherein said step portions include flat, radially outwardly facing surfaces defined by portions of said linear opposing sidewalls, and arcuate, radially inwardly facing surfaces defined by portions of said arcuate opposing sidewalls.
12. In a diffuser of a centrifugal compressor including an impeller, said diffuser including a plurality of tangentially disposed passages each having a throat portion of cross-sectional area A, the improvement comprising:
said throat portion having a quadrilateral cross section defined by two substantially parallel opposing linear sidewalls and two substantially arcuate opposing sidewalls, said two linear sidewalls being spaced from each other to define a minor dimension extending therebetween, said two arcuate sidewalls being spaced from each other to define a major dimension therebetween, said major dimension being greater in length than said minor dimension, said said linear sidewalls being disposed substantially normal with respect to a radial axis of said diffuser.
said throat portion having a quadrilateral cross section defined by two substantially parallel opposing linear sidewalls and two substantially arcuate opposing sidewalls, said two linear sidewalls being spaced from each other to define a minor dimension extending therebetween, said two arcuate sidewalls being spaced from each other to define a major dimension therebetween, said major dimension being greater in length than said minor dimension, said said linear sidewalls being disposed substantially normal with respect to a radial axis of said diffuser.
13. An improved diffuser according to claim 12 wherein said linear sidewalls are spaced from each other a distance 2b, each of said arcuate sidewalls is defined by a radius R extending from a center point of said throat portion, and wherein R, A and b are related to each other as follows:
14. An improved diffuser according to claim 13 wherein said distance b represents one half the tip width of blades of said impeller.
15. An improved diffuser according to claim 12 wherein said quadrilateral cross sections has an area and said linear opposing sidewalls are spaced from each other a distance less than the diameter of a circle having an area equal to said quadrilateral area.
16. A diffuser according to claim 12 wherein each of said inlet portions defines a partially bounded passage having a generally semi-circular cross section at an upstream end thereof which is open at opposing base and apex portions thereof, said inlet portion taper-ing from said semi-circular cross section to said first quadrilateral cross section of said throad portion.
17. A diffuser according to claim 16 wherein said adjacent ones of said inlet portions intersect with each other to define step portions extending and tapering from said throad portion to said upstream end of said inlet portion.
18. A diffuser according to claim 17 wherein said step portions include flat, radially outwardly facing surfaces defined by portions of said linear opposing sidewalls and arcuate, radially inwardly facing surfaces defined by portions of said arcuate opposing sidewalls.
19. A diffuser for a centrifugal compressor having an impeller comprising:
an annular housing;
a plurality of passages spaced about the circumference of said housing and extending therethrough, adjacent ones of said passages intersecting with each other at radially inner inlet portions thereof for defining a quasi-vaneless annular inlet of said diffuser, each of said passages further including a throat portion integral with said inlet portion, said throat portion having a first quadrilateral cross section including two substantially parallel linear opposing sidewalls and two substantially arcuate opposing sidewalls, said two linear sidewalls being spaced from each other to define a minor dimension extending therebetween, said two arcuate sidewalls being spaced from each other to define a major dimension therebetween, said major dimension being greater in length than said minor dimension, and said linear side-
19. A diffuser for a centrifugal compressor having an impeller comprising:
an annular housing;
a plurality of passages spaced about the circumference of said housing and extending therethrough, adjacent ones of said passages intersecting with each other at radially inner inlet portions thereof for defining a quasi-vaneless annular inlet of said diffuser, each of said passages further including a throat portion integral with said inlet portion, said throat portion having a first quadrilateral cross section including two substantially parallel linear opposing sidewalls and two substantially arcuate opposing sidewalls, said two linear sidewalls being spaced from each other to define a minor dimension extending therebetween, said two arcuate sidewalls being spaced from each other to define a major dimension therebetween, said major dimension being greater in length than said minor dimension, and said linear side-
Claim 19 continued: - 15 -walls being disposed substantially normal with respect to a radial axis of said diffuser;
said first quadrilateral cross section having an area and said linear opposing sidewalls being spaced from each other with said minor dimension being less than the diameter of a circle having an area equal to said first quadrilateral area;
each of said inlet portions defining a partially bounded passage having a generally semi-circular cross section at an upstream end thereof which is open at opposing base and apex portions thereof, said inlet portion tapering from said semi-circular cross section to said first quadrilateral cross section of said throat portion;
said adjacent ones of said inlet portions intersecting each other to define step portions extending and tapering from said throat portion to said upstream end of said inlet portion;
said step portions including flat, radially outwardly facing surfaces defined by portions of said linear opposing sidewalls and arcuate, radially inwardly facing surfaces defined by portions of said arcuate opposing sidewalls;
said throat portion extending with a constant area in a tangential direction for a length generally equal to the diameter of a circle having an area equal to the area of said first quadrilateral cross section of said throat portion;
said plurality of passages further including a diffuser portion integral with said throat portion and having at a downstream end a second quadrilateral cross section including two substantially parallel opposing linear sidewalls and two substantially arcuate opposing sidewalls;
said diffuser portion further including at an upstream end a third quadrilateral cross section substantially identical to said first quadrilateral cross section of said throat portion, said diffuser portion being gradually tapered between said upstream and down-stream ends; and said second quadrilateral cross section being oriented substantially 90 degrees with respect to said first quadrilateral cross section.
said first quadrilateral cross section having an area and said linear opposing sidewalls being spaced from each other with said minor dimension being less than the diameter of a circle having an area equal to said first quadrilateral area;
each of said inlet portions defining a partially bounded passage having a generally semi-circular cross section at an upstream end thereof which is open at opposing base and apex portions thereof, said inlet portion tapering from said semi-circular cross section to said first quadrilateral cross section of said throat portion;
said adjacent ones of said inlet portions intersecting each other to define step portions extending and tapering from said throat portion to said upstream end of said inlet portion;
said step portions including flat, radially outwardly facing surfaces defined by portions of said linear opposing sidewalls and arcuate, radially inwardly facing surfaces defined by portions of said arcuate opposing sidewalls;
said throat portion extending with a constant area in a tangential direction for a length generally equal to the diameter of a circle having an area equal to the area of said first quadrilateral cross section of said throat portion;
said plurality of passages further including a diffuser portion integral with said throat portion and having at a downstream end a second quadrilateral cross section including two substantially parallel opposing linear sidewalls and two substantially arcuate opposing sidewalls;
said diffuser portion further including at an upstream end a third quadrilateral cross section substantially identical to said first quadrilateral cross section of said throat portion, said diffuser portion being gradually tapered between said upstream and down-stream ends; and said second quadrilateral cross section being oriented substantially 90 degrees with respect to said first quadrilateral cross section.
20. A diffuser according to claim 19 wherein:
said impeller includes blades each having a tip width of 2b;
said first quadrilateral cross section of said throat portion has an area A;
said linear sidewalls of said first quadrilateral cross section are spaced from each other such that said minor dimension equals 2b;
said arcuate sidewalls of said first quadrilateral cross section are each defined by a radius R and said major dimension equals 2R; and said area A, said radius R, and said dimension b are related to each other as follows:
said impeller includes blades each having a tip width of 2b;
said first quadrilateral cross section of said throat portion has an area A;
said linear sidewalls of said first quadrilateral cross section are spaced from each other such that said minor dimension equals 2b;
said arcuate sidewalls of said first quadrilateral cross section are each defined by a radius R and said major dimension equals 2R; and said area A, said radius R, and said dimension b are related to each other as follows:
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/557,561 US4576550A (en) | 1983-12-02 | 1983-12-02 | Diffuser for a centrifugal compressor |
| US557,561 | 1990-07-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1233147A true CA1233147A (en) | 1988-02-23 |
Family
ID=24225930
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000468496A Expired CA1233147A (en) | 1983-12-02 | 1984-11-23 | Diffuser for a centrifugal compressor |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4576550A (en) |
| JP (1) | JPS60145499A (en) |
| CA (1) | CA1233147A (en) |
| CH (1) | CH668808A5 (en) |
| DE (1) | DE3442665A1 (en) |
| FR (1) | FR2556054B1 (en) |
| GB (1) | GB2150638B (en) |
| IT (1) | IT1221005B (en) |
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| KR950009062B1 (en) * | 1990-10-30 | 1995-08-14 | 캐리어 코포레이션 | Centrifugal compressor with pipe diffuser and collector |
| US5266002A (en) * | 1990-10-30 | 1993-11-30 | Carrier Corporation | Centrifugal compressor with pipe diffuser and collector |
| US5145317A (en) * | 1991-08-01 | 1992-09-08 | Carrier Corporation | Centrifugal compressor with high efficiency and wide operating range |
| JPH072428U (en) * | 1993-06-19 | 1995-01-13 | 有限会社三和 | Garland name tag cover |
| JPH07277347A (en) * | 1994-04-04 | 1995-10-24 | Shigeru Kobayashi | Nameplate cover |
| US6651439B2 (en) | 2001-01-12 | 2003-11-25 | General Electric Co. | Methods and apparatus for supplying air to turbine engine combustors |
| US6540481B2 (en) | 2001-04-04 | 2003-04-01 | General Electric Company | Diffuser for a centrifugal compressor |
| US6589015B1 (en) * | 2002-05-08 | 2003-07-08 | Pratt & Whitney Canada Corp. | Discrete passage diffuser |
| JP3815426B2 (en) | 2002-11-28 | 2006-08-30 | ヤマハ株式会社 | Piezoelectric transducer for stringed instruments, strings and stringed instruments for stringed instruments |
| US6854954B2 (en) * | 2003-03-03 | 2005-02-15 | General Electric Company | Methods and apparatus for assembling turbine engines |
| US7101151B2 (en) * | 2003-09-24 | 2006-09-05 | General Electric Company | Diffuser for centrifugal compressor |
| US8505305B2 (en) * | 2007-04-20 | 2013-08-13 | Pratt & Whitney Canada Corp. | Diffuser with improved erosion resistance |
| US7905703B2 (en) * | 2007-05-17 | 2011-03-15 | General Electric Company | Centrifugal compressor return passages using splitter vanes |
| US8235648B2 (en) | 2008-09-26 | 2012-08-07 | Pratt & Whitney Canada Corp. | Diffuser with enhanced surge margin |
| US8147178B2 (en) * | 2008-12-23 | 2012-04-03 | General Electric Company | Centrifugal compressor forward thrust and turbine cooling apparatus |
| US8087249B2 (en) * | 2008-12-23 | 2012-01-03 | General Electric Company | Turbine cooling air from a centrifugal compressor |
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| CN105793577B (en) * | 2013-12-05 | 2021-06-08 | 通用电气公司 | Curved diffuser passage section for centrifugal compressor |
| DE102015219556A1 (en) | 2015-10-08 | 2017-04-13 | Rolls-Royce Deutschland Ltd & Co Kg | Diffuser for radial compressor, centrifugal compressor and turbo machine with centrifugal compressor |
| US10570925B2 (en) | 2015-10-27 | 2020-02-25 | Pratt & Whitney Canada Corp. | Diffuser pipe with splitter vane |
| US9926942B2 (en) | 2015-10-27 | 2018-03-27 | Pratt & Whitney Canada Corp. | Diffuser pipe with vortex generators |
| US10352237B2 (en) | 2016-05-26 | 2019-07-16 | Rolls-Royce Corporation | Diffuser having shaped vanes |
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| CN107061368B (en) * | 2017-03-15 | 2018-12-11 | 清华大学 | Using the centrifugal compressor of the circumferential asymmetric vaned diffuser of variable-vane consistency |
| CN107061321B (en) * | 2017-03-15 | 2018-12-11 | 清华大学 | Using the compressor of the variable asymmetric vaned diffuser of established angle and consistency coupling |
| US10871170B2 (en) * | 2018-11-27 | 2020-12-22 | Honeywell International Inc. | High performance wedge diffusers for compression systems |
| US11333171B2 (en) * | 2018-11-27 | 2022-05-17 | Honeywell International Inc. | High performance wedge diffusers for compression systems |
| US11131210B2 (en) | 2019-01-14 | 2021-09-28 | Honeywell International Inc. | Compressor for gas turbine engine with variable vaneless gap |
| US11098730B2 (en) | 2019-04-12 | 2021-08-24 | Rolls-Royce Corporation | Deswirler assembly for a centrifugal compressor |
| US11286952B2 (en) | 2020-07-14 | 2022-03-29 | Rolls-Royce Corporation | Diffusion system configured for use with centrifugal compressor |
| US11441516B2 (en) | 2020-07-14 | 2022-09-13 | Rolls-Royce North American Technologies Inc. | Centrifugal compressor assembly for a gas turbine engine with deswirler having sealing features |
| US11578654B2 (en) | 2020-07-29 | 2023-02-14 | Rolls-Royce North American Technologies Inc. | Centrifical compressor assembly for a gas turbine engine |
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| US3719430A (en) * | 1971-08-24 | 1973-03-06 | Gen Electric | Diffuser |
| SE382342B (en) * | 1973-06-18 | 1976-01-26 | United Turbine Ab & Co | SEWER DIFFUSER FOR CENTRIFUGAL COMPRESSOR |
| US3860360A (en) * | 1973-09-04 | 1975-01-14 | Gen Motors Corp | Diffuser for a centrifugal compressor |
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| US4027997A (en) * | 1975-12-10 | 1977-06-07 | General Electric Company | Diffuser for a centrifugal compressor |
| JPS60898A (en) * | 1983-06-17 | 1985-01-05 | Toshiba Corp | Control device for returned sludge to digesting tank |
-
1983
- 1983-12-02 US US06/557,561 patent/US4576550A/en not_active Expired - Lifetime
-
1984
- 1984-11-09 GB GB08428339A patent/GB2150638B/en not_active Expired
- 1984-11-15 IT IT23597/84A patent/IT1221005B/en active
- 1984-11-23 FR FR848417860A patent/FR2556054B1/en not_active Expired - Lifetime
- 1984-11-23 CA CA000468496A patent/CA1233147A/en not_active Expired
- 1984-11-23 DE DE3442665A patent/DE3442665A1/en active Granted
- 1984-11-27 CH CH5659/84A patent/CH668808A5/en not_active IP Right Cessation
- 1984-11-29 JP JP59250690A patent/JPS60145499A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2556054A1 (en) | 1985-06-07 |
| JPH0514119B2 (en) | 1993-02-24 |
| IT8423597A0 (en) | 1984-11-15 |
| JPS60145499A (en) | 1985-07-31 |
| GB8428339D0 (en) | 1984-12-19 |
| CH668808A5 (en) | 1989-01-31 |
| IT1221005B (en) | 1990-06-21 |
| GB2150638B (en) | 1987-11-25 |
| US4576550A (en) | 1986-03-18 |
| DE3442665C2 (en) | 1993-09-16 |
| DE3442665A1 (en) | 1985-06-13 |
| GB2150638A (en) | 1985-07-03 |
| FR2556054B1 (en) | 1991-02-01 |
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